A waveguide guides waves such as electromagnetic waves through a medium with minimal loss of energy by restricting its expansion. Without the physical constraint of a waveguide, wave amplitudes decrease according to the inverse square law as they expand into three dimensional space. Accordingly, the waveguide guides optical waves by total internal reflection.
Polarization in a TM (transverse magnetic) transmission mode or a TE (transverse electric) transmission mode are important in photonic integrated circuits for optical sensing, communication, and signal processing, as examples. The principle of the polarizer is to make one polarization of one type of transmission mode more lossy than another type of transmission mode.
Current polarizers require different waveguide dimensions (e.g., height and width) to transmit in either the TE polarized mode or TM transmission polarized mode. This adds complexity in device fabrication. Also, constant-radius bend polarizers have junctions with opposite signs of curvature, which leads to mode mismatch and subsequent scattering, elevating the insertion loss of the polarizer.
Moreover, current TM pass polarizers require high aspect ratio waveguides which are challenging to fabricate and/or require different device layer height for different wavelengths. In addition, grating based TM pass polarizers suffer from strong back reflection, where the TE mode lies in the photonic bandgap of the grating.